Many oilfield operations occur with a fluid be circulated through or otherwise introduced into the borehole. These fluids may include drilling fluids that are circulated during the drilling of the well, completion fluids that may be circulated during or after drilling during various completion operations, and fracturing fluids which may be used after drilling in order to stimulate the well to increase production from a hydrocarbon reservoir.
After a well is drilled into a subterranean geological formation that contains oil, natural gas, and water, efforts are made to maximize the production of the oil and/or gas. To increase the permeability and flow of the oil and/or gas to the surface, the drilled wells are often subjected to well stimulation. Well stimulation generally refers to several post drilling processes used to clean the well bore, enlarge channels, and increase pore space in the interval to be injected thus making it possible for fluids to move more readily into the formation.
A well stimulation process may generally include pumping engineered fluids at high pressure and rate into the subterranean geological formation. The fluid (usually water with some specialty high viscosity fluid additives) exceeds the rock strength and opens a fracture in the formation, which can extend out into the geological formation for as much as several hundred feet. Certain commonly used fracturing treatments generally comprise a carrier fluid (usually water or brine) and a polymer, which is also commonly referred to as a friction reducer. Many well stimulation fluids will further comprise a proppant. Other compositions used as fracturing fluids include water with additives, viscoelastic surfactant gels, gelled oils, crosslinkers, oxygen scavengers, and the like.
Water may be used in all of these processes as a component of wellbore fluids, as well as in other types of fluids not specifically mentioned. However, the water used in wellbore fluids may contain microbes, such as bacteria, fungus, etc., that can grow and proliferate on the surface or downhole. Biocides and antimicrobials may be used to control microbial growth in the water. As used herein, “control” is defined to include both inhibition and removal. If left untreated, microbes and microbial biofilms (slimes) can cause deterioration of equipment, loss off efficiency in equipment, promotion and acceleration of corrosion on metal surfaces, or increased down time.